3 Rerunning Commands
3. Rerunning Commands
All the advice in this book will serve you better if you can type quickly. No matter how knowledgeable you are, if you type 40 words per minute and your equally knowledgeable friend types 120, they’re set up to work three times as fast as you. Search the web for “typing speed test” to measure your speed, then search for “typing tutor” and build a lifelong skill. Try to reach 100 words per minute. It’s worth the effort.
Linux Command Line Program: gtypist
Viewing the command History
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$ history
1000 cd $HOME/Music
1001 ls
1002 mv jazz.mp3 jazzy-song.mp3
1003 play jazzy-song.mp3
⋮ Omitting 477 lines
1481 cd
1482 firefox https://google.com
1483 history Includes the command you just ran
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$ history 3 Print the 3 most recent commands
1482 firefox https://google.com
1483 history
1484 history 3
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$ history | less Earliest to latest entry
$ history | sort -nr | less Latest to earliest entry
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$ history | grep -w cd
1000 cd $HOME/Music
1092 cd ..
1123 cd Finances
1375 cd Checking
1481 cd
1485 history | grep -w cd
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# To clear (delete) the history for the current shell:
$ history -c
Recalling Commands from the History
Cursoring Through History
up arrow key
down arrow key
Enter to run it.
On a full-sized American QWERTY keyboard, I place my right ring finger on the up arrow and my right index finger on Enter to tap both keys efficiently. (Try it.)
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$ echo $HISTSIZE
500
$ HISTSIZE=10000
Store unlimited commands by setting the value to
-1.
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$ HISTCONTROL=ignoredups
If the value is ignoredups (which I recommend), then repeated commands are not appended if they are consecutive.
Whenever an interactive shell exits, it writes its history to the file $HOME/.bash_history or whatever path is stored in the shell variable HISTFILE:
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$ echo $HISTFILE
/home/smith/.bash_history
The variable HISTFILESIZE controls how many lines of history are written to the file.
If you change HISTSIZE to control the size of the history in memory, consider updating HISTFILESIZE as well:
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$ echo $HISTFILESIZE
500
$ HISTFILESIZE=10000
History Expansion
Two exclamation points in a row (“bang bang”) evaluates to the immediately previous command:
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$ echo Efficient Linux
Efficient Linux
$ !! "Bang bang" = previous command
echo Efficient Linux The shell helpfully prints the command being run
Efficient Linux
To refer to the most recent command that began with a certain string, place an exclamation point in front of that string:
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$ !grep
grep Perl animals.txt
alpaca Intermediate Perl 2012 Schwartz, Randal
To refer to the most recent command that contained a given string somewhere, not just at the beginning of the command, surround the string with question marks:
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$ !?grep?
history | grep -w cd
1000 cd $HOME/Music
1092 cd ..
⋮
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$ history | grep hosts
1203 cat /etc/hosts
$ !1203 The command at position 1203
cat /etc/hosts
127.0.0.1 localhost
127.0.1.1 example.oreilly.com
::1 example.oreilly.com
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$ history
4197 cd /tmp/junk
4198 rm *
4199 head -n2 /etc/hosts
4199 cd
4200 history
$ !-3 The command you executed three commands ago
head -n2 /etc/hosts
127.0.0.1 localhost
127.0.1.1 example.oreilly.com
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$ !-3:p
head -n2 /etc/hosts Printed, not executed
$ !-3:p
head -n2 /etc/hosts Printed, not executed, and appended to history
$ !! Run the command for real
head -n2 /etc/hosts Printed and then executed
127.0.0.1 localhost
127.0.1.1 example.oreilly.com
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$ ls -l /etc | head -n3 Run any command
total 1584
drwxr-xr-x 2 root root 4096 Jun 16 06:14 ImageMagick-6/
drwxr-xr-x 7 root root 4096 Mar 19 2020 NetworkManager/
$ echo "!!" | wc -w Count the words in the previous command
echo "ls -l /etc | head -n3" | wc -w
6
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# History Expressions Don’t Appear in the Command History
$ ls Run any command
hello.txt
$ cd Music Run some other command
$ !-2 Use history expansion
ls
song.mp3
$ history View the history
1000 ls
1001 cd Music
1002 ls "ls" appears in the history, not "!-2"
1003 history
Never Delete the Wrong File Again
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$ alias rm='rm -i' Often found in a shell configuration file
$ rm *.txt
/bin/rm: remove regular file 'a.txt'? y
/bin/rm: remove regular file 'b.txt'? y
/bin/rm: remove regular file 'c.txt'? y
Verify. Before running
rm, runlswith the desired pattern to see which files match.1 2
$ ls *.txt a.txt b.txt c.txt
Delete. If the output of
lslooks correct, runrm !$to delete the same files that were matched.1 2
$ rm !$ rm *.txt
!$(“bang dollar”) means the final word that you typed in the previous command.
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$ head myfile.txt
(first 10 lines of the file appear)
$ rm !$
rm myfile.txt
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$ ls *.txt *.o *.log
a.txt b.txt c.txt main.o output.log parser.o
$ rm !*
rm *.txt *.o *.log
!* (Bang Star) matches all arguments you typed in the previous command.
Incremental Search of Command History
- At the shell prompt, press Ctrl-R (the R stands for reverse incremental search).
- Start typing any part of a previous command—beginning, middle, or end.
- With each character you type, the shell displays the most recent historical command that matches your typing so far.
- When you see the command you want, press Enter to run it.
Press Ctrl-R a second time. This keystroke causes the shell to jump to the next matching command in the history.
Here are a few more tricks with incremental search:
- To recall the most recent string that you searched for and executed, begin by pressing Ctrl-R twice in a row.
- To stop an incremental search and continue working on the current command, press the Escape key, or Ctrl-J, or any key for command-line editing, such as the left or right arrow key.
- To quit an incremental search and clear the command line, press Ctrl-G or Ctrl-C.
Command-Line Editing
Cursoring Within a Command
Cursor keys for simple command-line editing:
| Keystroke | Action |
|---|---|
| Left arrow | Move left by one character |
| Right arrow | Move right by one character |
| Ctrl + left arrow | Move left by one word |
| Ctrl + right arrow | Move right by one word |
| Home | Move to beginning of command line |
| End | Move to end of command line |
| Backspace | Delete one character before the cursor |
| Delete | Delete one character beneath the cursor |
History Expansion with Carets
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$ md5sum *.jg | cut -c1-32 | sort | uniq -c | sort -nr
md5sum: '*.jg': No such file or directory
$ ^jg^jpg
$ ^jg^jpg
md5sum *.jpg | cut -c1-32 | sort | uniq -c | sort -nr
⋮
Notice that the shell helpfully prints the new command before executing it, which is standard behavior for history expansion.
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s/source/target/
$ !!:s/jg/jpg/
$ !md5sum:s/jg/jpg/
Emacs- or Vim-Style Command-Line Editing
Vim-style editing:
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$ set -o vi
Emacs-style editing:
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$ set -o emacs
Keystrokes for Emacs- or Vim-style editing:
| Action | Emacs | Vim |
|---|---|---|
| Move forward by one character | Ctrl-f | l |
| Move backward by one character | Ctrl-b | h |
| Move forward by one word | Meta-f | w |
| Move backward by one word | Meta-b | b |
| Move to beginning of line | Ctrl-a | 0 |
| Move to end of line | Ctrl-e | $ |
| Transpose (swap) two characters | Ctrl-t | xp |
| Transpose (swap) two words | Meta-t | n/a |
| Capitalize word (uppercase first letter) | Meta-c | n/a |
| Uppercase to end of word | Meta-u | n/a |
| Lowercase to end of word | Meta-l | n/a |
| Change case of the current character | n/a | ~ |
| Insert the next character verbatim, including control characters | Ctrl-v | Ctrl-v |
| Delete forward by one character | Ctrl-d | x |
| Delete backward by one character | Backspace or Ctrl-h | X |
| Cut forward by one word | Meta-d | dw |
| Cut backward by one word | Meta-Backspace or Ctrl-w | db |
| Cut from cursor to beginning of line | Ctrl-u | d^ |
| Cut from cursor to end of line | Ctrl-k | D |
| Delete the entire line | Ctrl-e Ctrl-u | dd |
| Paste (yank) the most recently deleted text | Ctrl-y | p |
| Paste (yank) the next deleted text (after a previous yank) | Meta-y | n/a |
| Undo the previous editing operation | Ctrl-_ | u |
| Undo all edits made so far | Meta-r | U |
| Switch from insertion mode to command mode | n/a | Escape |
| Switch from command mode to insertion mode | n/a | i |
| Abort an edit operation in progress | Ctrl-g | n/a |
| Clear the display | Ctrl-l | Ctrl-l |
| Move ‘back’ through the history list, fetching the previous command. | Ctrl-p | |
| Move ‘forward’ through the history list, fetching the next command. | Ctrl-n |
https://www.gnu.org/software/bash/manual/html_node/Bindable-Readline-Commands.html
https://catonmat.net/ftp/bash-vi-editing-mode-cheat-sheet.pdf